Meiosis and Sexual Reproduction n n 2n Review Question Discussion Question
Jan 18, 2016
Meiosis and Sexual Reproduction
n
n 2n
Review Question
Discussion Question
Mitosis ReviewSingle-cell organisms (prokaryotic) carry
out Mitosis for asexual reproductionMulti-cell organisms (eukaryotics) carry
out Mitosis for growth and repairThe phases of mitosis in order are:
Prophase, Metaphase, Anaphase, and Telophase
Interphase is known as the “resting phase”
Cytokinesis occurs at the same time as telophase
Through which process do eukaryotic cells reproduce?
Requires sex cells from two parents (male and female)
Sex cells form as a result of meiosisOffspring are usually not identicalImportant for the survival of many
species◦Process results in genetic variation of
offspring
Sexual Reproduction
Define the following terms:
Sexual Reproduction
MeiosisGameteSomatic CellsHaploid
Textbook pg 46 - 51
• Fertilization• Zygote• Diploid• Homologous
Pairs
New Vocabulary
Meiosis: The process that results in the formation of gametes
Gametes: Sex cells (egg in females; sperm in males); contains haploid chromosomes
Somatic Cells: All body cells except for sex cells; contain Diploid chromosomes
Haploid: another term for half; refers to the number of chromosomes; written as n◦Chromosomes found singular
Fertilization: the union of an egg and a sperm
Zygote: Cell that forms as a result of fertilization◦Contains Diploid chromosomes (2n)
Diploid: Chromosomes found in pairs; written as 2n; Somatic Cells
Homologous Chromosomes: Similar chromosomes that are found in pairs; ½ of pair comes from mother, other ½ from father◦Human Body somatic cells contain 46
chromosomes, so 23 homologous pairs
MeiosisTwo division of the nucleus occursSteps of each division are similar to
those of mitosisMeiosis I
◦Each chromosome is duplicated, similar to mitosis
Meiosis II◦Two cells that form as a result of Meiosis I
divide again◦Four daughter cells are produced
Video
Meiosis
Parent cell – chromosome pair
Chromosomes copied
1st division - pairs split
2nd division – produces 4 gamete cells with ½ the original no. of chromosomes
Meiosis IPhase Image Description
Prophase I
- Homologous chromosomes pair together - Crossing over occurs between pairs resulting in genetic variation
Metaphase I
- Spindle fibers attach to chromosomes and line up in the middle of the cell
Anaphase I - Spindle fibers pull the homologous pairs apart- Chromosomes move to opposite sides of the cell
Telophase I
(& cytokinesi
s)
-Nuclear Membrane forms-Cell splits into two new cells- Cells contain haploid chromosomes (n)
Meiosis IIPhase Image Description
Prophase II
-new Spindle fibers form and attach to sister chromatids
Metaphase II
- Spindle fibers attach to sister chromatids and line up in the middle of the cell
Anaphase II
- Spindle fibers pull the sister chromatids apart- Chromosomes move to opposite sides of the cell
Telophase II(&
cytokinesis)
-Nuclear Membrane forms-Each cell splits into two new cells-Forms 4 haploid cells
What is the end result of Meiosis?
End Results of MeiosisFemale Eggs are MUCH larger than
male spermEach haploid cell in males become a
gamete◦Results in 4 sperm
Only 1 of the haploid cells in females become a gamete◦Results in 1 egg and 3 polar bodies◦Polar bodies are unused and broken down
K K K K
K K K K
EggPolar Bodies Why does
only one gamete form in Females?
How do Mitosis and Meiosis differ?
The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in
Meiosis
Mitosis The first (and distinguishing) division of meiosis
Crossing-Over
Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.
Explain the significant of crossing over.
Another Way Meiosis Makes Lots of Different Sex Cells
Another Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment
Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes.
That’s a lot of diversity by this mechanism alone.
In humans, n = 23 and 223 = 6,000,0000.
Meiosis – division error
Chromosome pair
Describe the errors that occur during each division.
Meiosis error - fertilization
Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’.
In humans this often occurs with the 21st pair – producing a child with Downs Syndrome
21 trisomy – Downs Syndrome
Can you see the extra 21st chromosome?